From the past, image display apparatuses such as a projector have been widely used. For example, light from a light source is modulated by a light modulation device such as a liquid crystal device, and the modulated light is projected onto a screen or the like so as to display an image. As the light source, a mercury lamp, a xenon lamp, an LED (Light Emitting Diode), an LD (Laser Diode), or the like is used. Of those, a solid-state light source such as an LED and an LD has advantages that a lifetime is long and thus lamp exchange as in the past is unnecessary and that the light source is lit immediately after power is turned on.
For example, Patent Literature 1 describes a light source device that uses a plurality of laser light sources, and an image display device that uses this. In the light source device described in Patent Literature 1, a light source part, a light collection optical system, a phosphor wheel, and a light-emitting lens are arranged in a casing. Blue laser light emitted from the light source part is collected on a phosphor provided on the phosphor wheel by the light collection optical system. By excitation, the phosphor converts a part of the blue laser light into yellow fluorescence and transmits another part of the light therethrough. As a result, white light obtained by synthesizing the blue laser light and yellow light is emitted via the light-emitting lens (paragraphs [0035] to [0039] of Patent Literature 1, etc.).